Metal rectifier element



Patented July 6, 1948 METAL RECTIFIER ELEMENT Hyman Samuel Denmark, NewYork, N. Y., as-

signor to Federal Telep hone & Radio Corporation, New York, N. Y., acorporation of Dela- Application July 13, 1943, Serial No. 494,457

(Cl. F75-366) 4 Claims.

1 This invention relates to metal rectiflers of the selenium plate typedesigned for use in series or stack assemblies wherein the electriccircuits are made through contact washers having pressure contactengagement with the electrodes of the respective plates. An importantobject of the present improvements is to produce, by a new method `ofmanufacture, an improved selenium rectifier plate' structure which inuse has important functional advantages materially contributing togreater durability and stability over long periods of use and inparticular to more successfully overcome certain objectionable factorspresent in the constructions of selenium rectifier plates as heretoforemade.

In present practice the selenium rectifier plates are composed of abacking plate, commonly of disc formation providing one electrode havingone face thereof coated with alayer of selenium forming an` imperfectconductor and over which is applied an alloy coating of good conductingmaterial forming the counter-electrode, the barrier layer for effectiverectification being formed between the selenium and the alloy coating inthe known manner. In the series assembling of the plates as now madespring contact washers are interposed between the plates and arranged toengage the opposite electrodes to establish the electrical connectiontherebetween.

In the assembled units as referred to there is present an objectionablecondition incident to the peculiar characteristic of the seleniumrectifier plate in that it is electrically affected by or susceptible topressure such that when pressure is exerted on its active area there isa tendency for an increase to take place in the reverse current therebyreducing its rectifying values. Limiting of the pressure contact toreduce this eniciency loss reduces the efliciency of the electricalcontact and is further objectionable when it is desired to moistureproof the rectifying unit by coating with a protective varnish whichwith limited pressure tends to penetrate between the contact washers andelectrodes.

While attempts have been made to remedy the objections aforesaid, forinst-anceas disclosed in Richards Patent 2,314,014 of March 16, 1943, bythe elimination of the active or barrier layer from the pressure area ofthe plates such attempts have been only partially successful in certainstructures under the condition of substantial clamping pressures toobtain good electrical contact, particularly from the tendency tofracture of the insulating layer'and of the counter-electrode alloy atthe region of the junction between the selenium and the insulation asthe result of varied compressivel strength of the diierent materials,non-uniformity in thickness resulting from manufacture and fromnon-uniformity of expansion and contraction from heating in use.

The present improvements comprise a structural arrangement employingrectifier plates of a further improved form having selenium andcounter-electrode materials' of uniform thickness and of homogeneousmaterials substantially coextensive with both the active, or barrier,area and with .the pressure protection areas thereof thereby providinggreater stability over long periods of use. This is accomplished by theemployment of an electrode base plate upon one side of which is appliedthe usual selenium powder layer while masking or covering a pressurecontact area and then, with masking of the first `applied layer,completing the layer over the pressure protection area with a specialselenium powder containing about .1% of thallium and pres'- sure andheat treating to unite with the plate.

The employment of this thallium content selenium without any halogenmakes this special selenium covered area an insulator so that there isno barrier or pressure responsive blocking area at the protectedportion. There is thereby provided a selenium layer of uniform thicknessand of homogeneousv material extending over both the active andprotected or insulated areas vand upon which the counter-electrode alloyis then sprayed as a covering of uniform thickness to be co-extensivewith both the active and protectively insulated areas thereof, thuspermitting pressure contact engagement with the electrodes withoutdanger Yof fracture and short circuiting and with elimination ofpressure effect' on the barrier layer. The homogeneous material layersof uniform thickness as thus provided fully eliminate the objectionsaforesaid such as danger of cracking result-ing from uneven thickness,non-uniform expansion -and unlike compressive strength of the insulatingmaterials as heretofore proposed.

The improved rectifier plate and method of manufacture will be morefully understood by reference to the accompanying drawing wherein likereference characters are applied to the corresponding parts in theseveral views.

In the drawing:

Fig. 1 is a central cross-sectional view through the base electrode dischaving a masking disc temporarily positioned thereon as a rst step inmanufacture;

therewith; l

r form thickness Fig. 4 is a similar view of the completed rectier platehaving the counter-electrode alloy applied over the selenium layer;

Fig.l 5 is a. face view of the completed rectifier plate of Fig. 4; p

Fig. 6 is a view corresponding to Fig. 4 showing a desirablemodification wherein the insulating selenium layer is thicker than theactive layer thereof and has overlapping relation thereto, and

Fig. 7 is a side elevation of rectifier assembly.

In the preferred embodiment of -the invention as here shown the baseelectrode I is in the form a portion of a typical of an annular flatiron 'disc having a central circular aperture 24 to receive thecustomary clamping bolt 0i the assembled unit having multiple plateswith interposed spring contact washers for series electrical connectionin the known manner. As made in accordance with the present improvedmethod, the base electrode, so formed, has temporarily applied to itsinner annular portion a masking disc 3 of circular form and of adiameter desirably slightly greater than that of the electrical contactwashers to be employed therewith. With the masking disc in positionthereon as shown in Fig. 1 the active selenium layer is applied inpowder form to the surface shown at 4 in Fig. 2 covering an annular areaoutwardly of the inn-er annular area protected by the masking disc 3.This inner area is-hereinafter referred to as the pressure area in thatit is subjected to the pressure of the electrical contact washers in thefinal assembly. The active selenium layer 4 referred to consists of theordinary selenium customarily applied in powdered form. Thereafter aninwardly continued layer of a special selenium powder is applied to thebase electrode by masking of the active selenium layer as shown indotted lines in Fig. 2. The continuous, combinedy selenium and specialselenium layer is then subjected to pressure and heat treating to unitewith the plate I in the customary manner. shown in Fig. 3 extends theselenium layer over the inner pressure area at 6 of uniform thicknesswith the active layer and is of a special selenium containing .1% ofthallium as referred to. This pressure area layer having thalliumcontent without any halogen makes the selenium layer of this inner areaan insulator and accordingly an inactive area as related to blockingeffect and correspondingly non-pressure sensitive in influence on therectification thereby to permit pressure contact at this portion withoutaffecting proper operation and avoiding possible damage to the barrierarea. As shown in Fig, 4, the'counter electrode alloy layer 8 is in theusual manner lapplied by spraying to cover substantially the full activeselenium area and to be of uniform thickness, and the disc is thenprocessed for the electro-forming of the barrier layer. There is thusprovided an improved rectifier plate having uniselenium andcounter-electrode layers and wherein the'selenium layer includes ahomogeneous portion, or continuation of the active area, of insulatingcharacter positioned to receive and resist the pressure of theelectrical contact washers in an area removed from the barrier formationwith the substantial benefits as described.

In Fig. 6 there is shown a desirable modification wherein the pressurearea layer of selenium 6 of insulating properties is thickened relativeto that of the outward active selenium of the plate as` ing a baseelement layer and is applied to the plate to be overlapping in relationto the active layer at the outer marginal portion of the insulation. Inconnection therewith the electrical contact washer is shown at I0 tohave a contact area of slightly smaller diameter than that of theinsulating selenium area, of major thickness thereby avoidingcompressive stresses at the selenium junction or area of overlapping.

What is claimed is:`

1. In a selenium rectifier of the type comprisbearing a selenium layer`carrying a counter-electrode and adapted to being supported inoperating'condition by application of pressure against a portion of thesurface of said counter-electrode, the improvements that compriseinterposing between the base element and the counter-electrode in thezone underlying the portion of the counter-electrode against whichpressure is applied, an electrically insulative body comprising seleniumhaving thallium f admixed therewith, .the thallium content of said Thiscontinued layer as Icomprising a metallic disc body being in the orderweight.

2. In a selenium rectifier loi' 0.1% based upon element of the typecarrying a layer of selenium with a superposed counter-electrode andadapted to being mounted upon a spindle extending through a centrallylocated opening, said element when in use being subjected to pressureapplied to the counter-electrode in the region near said opening, theimprovements that coinprise interposing between the counter-electrodeand the disc in said Yregion an electrically insulative body comprisingselenium containing thallium in an amount of the order of 0.1% basedupon Weight.

3. In a selenium rectifier element of the type vcomprising a, metallicdisc bearing a selenium layer with an overlying counter-electrode,adapted to being supported under pressure applied in a region adjoininga centrally located opening formed in the element, the improvement thatcomprises interposing'between the disc and the counter-electrode, in anannular zone adjacent the centrally located opening, an electricallyinsulative mass of selenium containing about 0.1% by weight of thallium.

4. In a process for the manufacture of selenium rectiers wherein aselenium layer is applied to a metallic base plate and a`counter-electrode is thereafter applied to the selenium layer andwherein an electrically insulative body is interposed in a localizedportion of the selenium layer between the counter-electrode and the baseplate, the improvement that comprises forming said electricallyinsulative body of selenium containing about 0.1% of thallium based uponweight.

HYMAN S. DENMARK.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,157,895 Hein May 9, 19392,182,377 Guanella Dec. 5, 1939 2,215,999 Brunke Sept. 24, 19402,235,051 Thompson Mar. 18, 1941 2,244,664 Addink June 10, 19412,279,746 Thompson Apr- 14, 1946 2,314,104 Richards et al Mar. 16, 19432,343,379 Kotterman Mar. 7, 1944

